Sewage and drainage systems typically use underground pipes to convey sewage, storm water, and other waste material to a treatment facility or waste disposal site. These pipes are routed through manholes at various locations. Manholes are used to provide access to the system for cleaning and repair. Manholes are also used when there is a change of grade or direction to maintain the proper flow of waste material.
In the past, sewage pipes have been formed of concrete. These concrete pipes were attached into the manhole and sealed in place with cement grout. Because concrete pipes are porous, they frequently do not remain watertight. In addition, concrete pipes tend to fracture when improperly backfilled. Because of public health concerns, regulations in many localities require that plastic or PVC pipe be used instead of concrete, and that all pipe connections achieve some degree of watertightness.
The use of plastic pipe with concrete manholes makes it very difficult to obtain a proper seal where the two come together because of the incompatibility of plastic and concrete. In one proposed method for overcoming this problem, a concrete cylinder with an axial bore is formed and a gasket is then rolled inside the bore. In some instances, the gasket is held in position in the bore by cutting a channel around the inside of the bore and then rolling the gasket in place in the channel.
This method has several disadvantages. First, when the plastic pipe is backfilled with soil, the weight pushing down on the pipe causes the pipe to crush the gasket at the bottom of the pipe, leaving a gap between the top of the pipe and the gasket. This gap also occurs when the pipe is not positioned perpendicular to the seal. In addition, the weight of the backfill causes movement of the pipe, which can crack the cylinder. As a result, these cylinders frequently fail to achieve or maintain a watertight connection. Furthermore, cutting a channel inside the bore of the pipe requires the use of carbon- or diamond-tipped cutting tools. This type of machining is expensive, time-consuming, and can weaken the concrete. The present invention is directed to overcoming these drawbacks.